This is a continuing investigation of the relationship between composition and particle size variables in amalgam alloy powders and the properties of the resultant amalgams. The approach involves the determination of a broad series of properties on spherical alloy powders of known composition and particle size distribution. These factors and manipulative variables such as Hg:alloy ratio will be studied relative to micro-structure and properties. Metallography, microprobe and x-ray diffraction techniques will be used to study structure, while primary emphasis will be on setting expansion and rheologic properties. During the current year emphasis is to be placed on determinations of rate of mercury consumption and on the variables determining to amount, composition and distribution of the copper-tin phases formed in copper containing amalgams.